The switch-on actuating force generator of the seated-type valve of this kind according to DE 33 45 720 C is constituted by a piston-like integrated prolongation of the slider closure element, which prolongation is guided in sealed fashion in a small diameter section of the prolonged housing bore. The separation actuation force generator uses an integrated tube-like prolongation of the slider closure element situated in another prolonged section of the housing bore. Several drawbacks result from this design. The structural length of the slider closure element is large and results in an extremely long seated-type valve. A further disadvantage is that the sections of the bore used for the piston-like prolongation and the tube-like prolongation of the slider closure element have to be aligned particularly precisely with the valve seats in order to allow to displace smoothly the slider closure element without hindering lateral forces. This precise alignment only can be achieved by considerably high manufacturing efforts resulting in high manufacturing costs. This alignment, furthermore, hardly can be achieved reliably within a series of seated-type valves, because the housing has to be made from at least two parts to allow the mounting of the one piece slider closure element. Finally, the functionally important precise alignment cannot be maintained reliably during a long service life. The switching time durations are undesirably extended, since the structural length is large and a relatively big oil quantity has to be displaced over long distances during the switching cycles. For electric disconnectors, however, a cycle time of only several milliseconds is required particularly when switching the disconnector into the separating position. As production depending fluctuations cannot be excluded, which increase the displacement resistance of the slider closure element and which are detrimental for a correct alignment of the components as mentioned above, large pressure actuated areas are provided for safely generating sufficiently strong actuating forces further increasing the oil quantities which have to be moved during the switching cycles. For example, a large oil quantity has to be pressed back by the separating actuating force generator into the pump port and from the pump port through the first still strongly throttling pump valve seat into the cylinder port, when switching over from the separating position into the switch on position. This extends the switch-over time duration undesirably.
The housing of the seated-type valve known from EP 00 74 419 B is one piece while the slider closure element is assembled of two pieces. Both valve seats are of equal size. Both actuating force generators have pistons of differing sizes which are separated by the slider closure element and are slidably guided in the housing in the prolongation of the slider closure element The pistons are thus able to generate the actuating forces for the slider closure element without hindering lateral forces. For that reason, no precise alignment is necessary between the housing bore sections receiving the pistons and the housing bore section guiding the slider closure element However, as the pistons operate in prolongation of the slider closure element the valve itself has to have an undesirably large structural length. The divided design of the slider closure element is complicated. During the switching cycles relatively large oil volumes have to be moved over long distances.
It is an object of the invention to provide a structurally simple seated-type valve of the kind as disclosed above which is compact in moving direction of the slider closure element, which operates reliably during a long service life and in which during the switching cycles only minimum oil volumes are displaced over short distances.
The piston uses a part of the longitudinal extension of the slider closure element and does not protrude significantly beyond the slider closure element as it is operating in a telescopic fashion directly within an interior bore of the slider closure element This design allows to considerably reduce the structural length of the seated-type valve in the direction of the movement of the slider closure element The piston generates the separating actuating force for the slider closure element without hindering lateral forces such that the slider closure element is smoothly movable against very low displacement resistance. This safe operational behaviour can be achieved by a moderate manufacturing effort and in a cost effective way. Since the safety of constant low displacement forces of the slider closure element is unexpectedly high even during a long service life up to e.g. 30 years weak holding actuating forces for both end positions of the slider closure element may be set. This means that the first and second and pressure actuated surfaces are small-sized and advantageously can be designed (xe2x80x9criskyxe2x80x9d) in terms of their mutual relative dimensional relationship and their relationship to the pressure actuated areas of the valve seats. Due to such small sized pressure actuated areas, however, only small oil volumes have to be moved over short distances during the switching cycles.
In an advantageous embodiment the pump seat area is larger than the tank seat area while the first pressure actuated area is made smaller than the second pressure actuated area. From these dimensional relationships short switching time durations for both switching directions and minimal moved oil volumes will result.
The second pressure actuated area is only about twice as large as the first pressure actuated area. Due to the constant smooth mobility of the slider closure element without hindering lateral forces and due to the low actuating forces in comparison with the risk-free high actuating forces of conventional seated-type valves of this kind a very small-sized first pressure actuated area suffices for a proper function. As a consequence, the second pressure actuated area can be of relatively small size as well. Minimal oil volumes then need to be moved.
The second pressure actuated area may be only about more than 20% bigger than the dimensional difference between both valve seats, resulting in short switching time durations of the disconnector. The tank valve seat, e.g., is about 12% smaller than the pump valve seat.
The structural length even can be decreased further when the switch on actuating force generator is provided with its own slidably guided piston which may, e.g., be supported in the housing without the possibility to generate lateral forces for the slider closure element Since the actuating force is imparted on the slider closure element without lateral forces the slider closure element may operate in the housing with a relatively short guided length. The resulting gain of longitudinal extension can be used to structurally integrate the second piston without an Increase of the structural length.
When the piston having the second pressure actuated area is inserted into an Interior bore of the slider closure element the structural length of the seated-type valve even can be reduced considerably, since the piston actually does not need to protrude beyond the slider closure element in the retracted position. In this case, two sealing zones are needed for the slider closure element within the housing bore. In case that the piston defining the second pressure actuated area is Inserted into an interior bore of the housing, then a single sealing zone of the slider closure element will suffice in the housing bore. This contributes to the easy and smooth mobility of the slider closure element such that relatively low actuating forces will suffice to reliably displace the slider closure element rapidly enough.
At least one circumferential sealing is expediently provided at the piston and for co-operation with the inner wall of the interior bore. The circumferential sealing can be positioned between supporting rings.
In order to safely exclude hindering lateral forces at the slider closure element the piston should be convexly rounded at least at one of the ends which end actuates the housing or the slider closure element, respectively. Optimally, even a sliding shoe is provided at this end of the piston.
In an alternative the switch on actuating force generator may use an annular surface provided as the second pressure actuated area at the slider closure element itself. The annular surface expediently may be provided in the guiding section of the slider closure element without increasing the structural length thereof.
The seated-type valve expediently is a screw-in cartridge for Insertion into an outer housing. This design is compact, facilitates the assembly, assures high tightness, and allows to use high quality material, e.g. hardened steel, only for the screw-in cartridge. The high quality material can be machined precisely and assures the permanent easy mobility of the slider closure element. To the contrary, the outer housing may consist of a lower quality material available for lower costs such that the entire costs of the seated-type valve can be kept at a moderate level.
The screw-in cartridge expediently is provided with two steel sleeves located behind each other. This simplifies the manufacture and the assembly. Each steel sleeve may be machined alone and may consist of high quality material. This allows to harden and grind e.g. the guiding sections of the housing bore and the valve seats. The material choice and the treatments allows to reliably use the valve over a long service life, e.g. up to 30 years.
For an easy manufacture it is expedient to form the housing of two parts and to form the slider closure element as one piece only.